Problem: $\dfrac{3}{4} - \dfrac{6}{12} = {?}$
$ = {\dfrac{3 \times 3}{4 \times 3}} - {\dfrac{6 \times 1}{12 \times 1}} $ $ = {\dfrac{9}{12}} - {\dfrac{6}{12}} $ $ = \dfrac{{9} - {6}}{12} $ $ = \dfrac{3}{12}$